The present invention relates to a method for preparation of fine crystal of quinacridone pigment by use of high temperature high pressure solution, in particular relates to a method for preparation of fine crystal of quinacridone pigment by means of a reprecipitation method from supercritical or sub-critical liquid. Further, the present invention relates to a method for preparation of fine crystal of quinacridone pigment having adjusted submicron average particle size by following process. Namely, supercritical or sub-critical liquid is provided continuously into a specimen tube composing of a reactor with a filter which prevents the flow out of the material quinacridone pigment, the supercritical or sub-critical liquid of quinacridone pigment is took out by way of said filter to a mixing apparatus in which said liquid is mixed with coolant and is reprecipitated. The preparation of above mentioned fine crystal of quinacridone pigment is carried out by using, for example, a flow type apparatus mentioned in FIG. 1.
The quinacridone pigment, for example, the non-substituted quinacridone pigment or 2,9-dimethyl quinacridone has a good light absorption and has less impulse to skin, namely has high biological security, further, is a stable red pigment to heat and light. Therefore, the quinacridone pigment is used as an excellent coloring agent for a coating, a color filter, a toner for electrophotography, a developer or an ink for jet printing. Further, since the quinacridone pigment has a functional characteristic such as an excellent electro static characteristic or an light-electric characteristic, it is used as an additive for improving the electret characteristic, an EL material or as an electric charge generating layer forming material in organic photo semiconductor material for photosensitive medium of electrophotography.
Still more, the other quinacridone pigment, e.g. 2,9-dimethyl qulnacridone, 2,9-dichloroquinacridone, 2,9-difluoroquinacridone, 2,9-dimethoxyquinacridone or 4,11-dichloroquinacridone can adjust the particle size, color characteristic or electrostatic characteristic of the obtained solid by forming solid solution (or mixed crystal) with non-substituted quinacridone pigment, or 2,9-dimethyl quinacridone, and then can be used as the material to generate the quinacridone pigment whose uses are improved.
The useful characteristics that said organic quinacridone pigment has, such as disparsability, reoligical characteristic, photo characteristic, absorption wave length (coloring ability) or transparency are affected by purity, size of crystalline particle, particle size distribution and shape of the particle, and the functional characteristic is changed. Therefore, it is important to develop the method for crystallization which can adjust the crystal particle according to the desired characteristic.
Usually, for the adjusting of the particle size of quinacridone pigment, the mechanical grinding method by dry condition (sand grind, ball mill) or by wet condition (salt-kneading), and the method by solvent treatment, for example, the method to heat with solvent (under the presence of water or additives such as dispersing agent or surface active agent) are proposed.
Further, the technique to adjust the particle size of quinacridone pigment by contriving the manufacturing process of said pigment is also proposed. For example, the technique by finding out the particle growth controlling molecule which is especially effective for the growth of pigment particle and/or for the controlling and adjusting of crystal modification and by making coexist said molecule in the process to manufacture the quinacridone pigment is reported UP Laid-open publication 2000-226530, published on Aug. 15, 2000). Said technique is illustrated as follows, namely, the particle growth controlling molecule is absorbed to the synthesized pigment molecule and accordingly controls the growth of crystal and crystalline phase. And it is illustrated that, by this technique, the growth of crystal can be controlled by generating a desired crystalline phase shape, for example, fine plate crystal, needle crystal, cubic crystal, small leaf form crystal, prism crystal, fibrous crystal or other geometric shape.
As mentioned above, because of the usefulness of quinacridone and derivatives thereof, the quinacridone and derivatives thereof are not only used for approximately 50% of all red pigments, but also is promisingly used for EL materials. However, the conventional technique to adjust the particle size of crystal of quinacridone pigment can not be said sufficient as the technique for the preparation of fine particle of quinacridone pigment with desirable characteristic, further linked to the development of the novel function. Further, because the quinacridone pigment is an insoluble compound, it is very difficult to find out the solvent which can be used effectively to the preparation of crystal by means of re-crystallization (re-precipitation), and the refinement and the crystallizing of it are not so easy.
The object of the present invention is to provide a method for preparation of quinacridone pigment by which the refining and the crystallization of quinacridone pigment can be can easily carried out under the regulated condition.
The inventors of the present invention are proposing the technique relating to a method for preparation of organic fine crystals such as titanilphthalocyanine (TiOPc), one of polydiacetylene: 1,6-dicarbazoil-2,4-hexadlyne (Document 1), C60 (Document 2) and so on using supercritical liquid, further, are proposing the technique relating to a method for preparation of regulated fine crystal which can be used as nonlinear optical materials and switching materials (Document 3).
During an earnest study to dissolve the problems for refining and nanocrystallizing of above mentioned quinacridone pigment, the inventors of the present invention have tried to prepare the fine particle of quinacridone pigment using supercritical or sub-critical liquid. And the inventors of the present invention have found that by arranging the starting material for quinacridone pigment into a vessel in which the supercritical or sub-critical liquid flows, and by using an apparatus for supercritical re-precipitation which allows the flow of the supercritical or sub-critical liquid, the quinacridone pigment is refined as the first step, then, the fine crystal of quinacridone pigment whose particle size is adjusted can be simply and easily prepared in the state of water dispersion. And the problems of the present invention can be dissolved. That is, by altering the preparing condition such as kinds of supercritical or sub-critical liquid, supplying speed of the liquid, temperature of the liquid or pressure, it becomes possible to adjust the size (average particle size) of generated fine crystal particle within the range of particle size smaller than 500 nm, further within the range of particle size smaller than 300 nm. The phenomenon that the photo absorption characteristics are changeable along with the minimization of the particle size, is confirmed in the case of this quinacridone pigment too.
The present invention is the method for preparation of sub micron to nano size fine crystal of quinacridone pigment whose average particle size is regulated comprising, supplying supercritical or sub-critical liquid, which can dissolve quinacridone pigment, into a reactor containing quinacridone pigment, flowing out the supercritical or sub-critical liquid in which quinacridone pigment is dissolved from said reactor to a mixing apparatus to which coolant is supplied, and by selecting the kind of supercritical or sub-critical liquid and by selecting the combination of supplying speed of each liquids, temperature of the liquid and the reacting pressure. Desirably, the present invention is the method for preparation of said fine crystal of quinacridone pigment, wherein the reactor containing quinacridone pigment possesses a filter of 0.5 xcexcm to 20 xcexcm diameter to the upper stream side and to the down stream side. More desirably, the present invention is the method for preparation of fine crystal of quinacridone pigment whose average particle size is smaller than 300 nm, wherein the supercritical liquid at least one liquid selected from the group consisting of water, alcohol and ketone. Furthermore desirably, the present invention is the method for preparation of fine crystal of quinacridone pigment whose average particle size is smaller than 300 nm, wherein the coolant is at least one liquid selected from the group consisting of water, alcohol and ketone, the temperature of the coolant is adjusted to the range from xe2x88x92100xc2x0 C. to 50xc2x0 C. and the coolant is mixed with the supercritical liquid so as the volume ratio of supercritical liquid/coolant to be within the range from 1:1to 1:10. Still further desirably, the present invention is the method for preparation of fine crystal of quinacridone pigment whose average particle size is smaller than 300 nm of claim 4, wherein the supercritical liquid is water and the temperature of the supercritical liquid is from 270xc2x0 C. to 320xc2x0 C.